Nickel-silicon alloy product



Feb. 6, 1968 P. P. TURILLON ET AL 3,367,773

NICKIPSILICON ALLOY PRODUCT Filed May 5, 1965 @a y fc mm n ww; 3% @ses pm QNS H w w W O8@ ,V M QQ@ United States Patent O 3,367,773NICKEL-SILICON ALLOY PRODUCT Pierre P. Turillon, Ramsey, NJ., Robert R.Crawford,

Suffern, NY., and Dale T. Peters, Ringwood, NJ., assignors to TheInternational Nickel Company, Inc., New

York, N.Y., a corporation of Delaware Filed May 3, 1965, Ser. No.452,624 4 Claims. (Cl. 75-170) ABSTRACT OF THE DISCLOSURE Directed to anew coinage material having a particularly advantageous combination ofproperties for coinage purposes, such properties include a low Curietemperature, good workability, both hot and cold, good ernbossability,high resistance to corrosion, tarnishing and wear, controlledresistivity and density, and a bright silvery color; the material beingmade of a nickel-silicon alloy containing about 5% silicon.

The present invention is directed to an improved coinage alloy and, moreparticularly, to a nickel-base alloy coinage material having anoutstanding combination of coinage properties and characteristics.

Metallic coins have been in use for centuries and it is fair to say thatmetallic coinage is essential for the purpose of transacting business inany advanced civilization. The problems of producing a satisfactorycoinage are many and diverse, although these problems usually are takenfor granted since coins and their usage are an integral part of dailylife. The issuance of metal coinage has from earliest times been aprerogative of the sovereign and it has always been considered that fromthe standpoints of public acceptance of, and confidence in, the coinagethat the use of metals having substantial intrinsic value and goodappearance would be required. Many different metallic alloys, includingbronze and other copper alloys, gold, silver, nickel and nickel alloys,and other allows have been used in coinage from time to time dependingupon a myriad of factors. In modern times, the use of gold in coinagehas disappeared and recent technical advances pertaining to theindustrial uses of silver have created such a demand for this metal thatconsideration is being given to the replacement of silver as a coinagemetal.

Another fairly recent occurrence which has affected the use of coinagein the United States and other countries is the widespread adoption ofcoin-operated vending machines. While such machines have been in use foryears, their acceptance for a great variety of vending purposes has beenincreasing at an accelerating rate in recent times. One of the resultsof the relatively recent accelerated use of vending machines has been anacuate shortage of coins in the United States.

j The metallurgical requirements which must be met in providing asatisfactory coinage material, even absent the factor of vendingmachines, are stringent. Thus, the coin should be bright and resistantto tarnishing in order to secure public acceptance. For example,aluminum has been employed in certain countries for low denominationcoinage but this metal becomes dull and unattractive in appearanceduring handling in circulation and, furthermore, it has a poor ringwhich makes it unattractive and undesirable as a coinage material.Another example of an ersatz coinage material is the zinc plated steelone cent coin which was employed in the United States due to exigenciesof the wartime period. The appearance of these coins deterioratedrapidly during the circulation thereof and they were withdrawn fromcirculation. In addition, the coinage metal should be capable of readyprocessing "ice into strip. This factor imposes the requirement of goodhot and cold malleability, the ability to take a go-od surface upon coldrolling, and the capability of being embossed in the coinage dies toproduce a sharp, clear impression thereon. These additional requirementsfurther limit the choice of a coinage metal to materials having highductility and workability.

The introduction and use of coin-operated vending machines, which hastaken place at an accelerated rate, cornplicates the coinage problemeven further. Thus, it has been an altogether too common practice forunscrupulous individuals to attempt to operate vending machines by meansof spuri-ous or counterfeit coins, slugs, etc. While such attempts havebeen many and ingenious, the vending machine art has for the most partkept ahead of the counterfeiter and cheater by means of coin rejectormechanisrns which are carefully constructed so as to discriminatebetween valid coins and counterfeits or slugs. The Widespread usage ofvending machines, which have built into them coin-discriminating devicesof a highly sophisticated nature, now makes it advisable that anycoinage material which would be used as a substitute for present daycoinage materials be accepted in vending machines to the same degree aspresent day coinage alloys. Thus, the still further factor ofinterchangeability with present coinage alloys is advisable for anyproposed new coinage alloy because of the present very large investmentin vending machines. The coin-discriminating devices which have comeinto use in coin-operated vending machines subject the coin to a numberof tests which measure the coin for weight, size, electricalresistivity, hardness, and magnetic properties. For example, thediscriminating circuits employed in common vending machines designed toaccept the present day -cupronickel (about copper, balance nickel)United States five cent coin are equipped with a. slot which guides theinserted coin through a device which tests the coins for size andthickness. improperly dimensioned coins or slugs are rejected and, ifthe coin is perforated, it will be caught by a hook located in the pathof travel and be discarded. Coins which pass these tests are thencarried over a transfer cradle which checks the Weight. At this point,low-density or underweight coins are rejected. lf it is still acceptableafter these tests have been performed, the coin is rolled down a runwaythrough a magnetic field which checks the electrical resistivity andmagnetic properties of the coin. Thus, if the coin is stronglyferromagnetic, eg., steel, pure nickel, etc., it will be held by themagnet and thus prevented from freeing the vending machine mechanism.Thus, acceptable coins must be essentially nonmagnetic. Again, if theelectrical resistivity is not within a carefully dened range, the coinwill be rejected by the mechanism. Thus, the speed of the coin down therunway through the magnetic field is affected by induced eddy currentswith coins of lower electrical resistivity being slowed during passagedown the runway to a greater extent than coins of higher resistivity. Atthe end of the runway past the magnet, the coin follows a parabolictrajectory, hits a striker plate, and rebounds. If the coin isunsatisfactory in terms of its electrical resistivity or its hardness,it will not follow the prescribed trajectory beyond the striker plateand will accordingly be rejected. The five cent coin circuit in vendingmachines is set to accept properly dimensioued coins made of acupronickel alloy containing about 75% copper, balance nickel, having adensity of about 8.9, an electrical resistivity of about 30 to 35microhm-centimeters, and a Curie tem-- perature below about zero degreesF.

We have now discovered a new nickel-base coinage material which isaccepted by coin-discriminating devices designed to pass cupronickelcoinage such as the standard U.S. live cent coin and many foreign coins,and which posssesses to an outstanding extent desirable coinageproperties o-f appearance, resistance to tarnishing, hot and coldmalleability, ability to receive a sharp impression in coining dies, lowCurie point, controlled resistivity, wear resistance, and intrinsicvalue.

It is an object of the present invention to provide a nickel-base alloycoinage material having an outstanding combination of properties,including controlled resistivity, low Curie temperature, high wearresistance, good appearance, and resistance to tarnishing.

It is a further object of the invention to provide nickelbase alloycoins having a sharp embossed impression, good appearance, resistance totarnishing and interchangeability with standard cupronickel coinagematerial.

It is still another object of the invention to provide coinage strip andcoins having superior wear resistance and resistance to tarnishing ascompared to standard cupronickel alloy coinage materials.

Other objects and advantages of the present invention will becomeapparent from the `following description taken in conjunction with theaccompanying drawing which depicts the results of an acceleratedwear-corrosion test as applied to the coinage material of the invention.

Generally speaking, the present invention is directed to coinage stripand coins made of a special nickel alloy containing about 4.85% to 5.6%silicon with the balance of the alloy being essentially nickel. Moreadvantageously, the alloy contains about 4.85% to about 5.15% siliconsince such alloys are characterized by a resistivity which does notexceed about 40 microhm-centimeters, e.g., about 35 to about 40microhm-centimeters, and coins made thereof are interchangeable incoin-discriminating devices having a resistivity test designed to acceptcupronickel coins such as the U.S. five cent piece. yIn addition, suchmore vadvantageous alloys possess high ductility in that strip madetherefrom can be bent 180 degrees about a radius equal to the thicknessof the strip without cracking. In addition, such alloys arecharacterized by a broad hot working range and by freedom from edgecracking on rolling whereas with silicon contents exceeding about 5.6%edge cracking of hot rolled strip has been observed.

The coinage strip and coins contemplated in accordance with theinvention are made of an essentially binary nickel-silicon alloy havinga carefully controlled silicon content as described hereinbefore. Thealloy contains about 0.02% carbon, eg., 0.01% to about 0.05% carbon,less than about 0.1% iron, less than 0.2% cobalt, and less than about0.1% manganese. In common with other high-nickel alloys, the sulfurcontent of the alloy is maintained as low as possible and does not, inany event, exceed about 0.01% so as to avoid the detrimental effect ofsulfur on the malleability of the alloy. For the same reason, thecontents of impurities such as lead and phosphorus are maintained -belowabout 0.01% each. Carbon, iron and cobalt detrimentally affect therequired properties possessed by the coins and coinage stripcontemplated in accordance with the invention. Thus, carbondetrimentally raises the electrical resistivity of the material. Cobaltand iron detrimentally raise the Curie transition temperature. Thisfactor requires that high purity silicon be employed in preparing thealloy. Common ferrosilicon alloys are not satisfactory. The alloy may bedeoxidized by means of elements such as aluminum and magnesium butresidual quantities of these deoxidizers in the coinage material doesnot exceed about 0.1% each. Copper is maintained at low levels notexceeding about 1%, since the presence of copper in any materialquantity limits the silicon range, raises the hardness, and makes itexceedingly diicult to provide a nickelsilicon alloy coinage materialhaving the required low Curie temperature coupled with a resistivity notexceeding about 40 microhm-centimeters.

The special coinage material contemplated in accordance with theinvention is characterized by excellent hot workability and coldworkability which facilitates the production of coinage strip.

The special coinage material can be produced in conventional air meltingequipment and can -be reduced to strip using conventional forging, hotrolling, annealing, and cold working techniques. While it isadvantageous, as noted hereinbefore, to maintain the silicon content inthe special nickel coinage material within the limited range of 4.85% to5.15%, it is found in practice that this silicon range can be metrepeatedly and on a commercial scale. The close control of the siliconcontent which is required makes counterfeiting coins made of the specialalloy a diicult matter since technical control of the melting operationis required. Coinage strip and coins produced in accordance with theinvention possess to a remarkable degree a combination of mechanical andphysical properties which makes the material exceedingly useful incoinage service. Thus, coins produced in accordance with the inventionhave a bright, slivery color and have a good ring which is superior tothe cupronickel alloy currently employed in the production of the U.S.five cent piece. In addition, the alloy is nonmagnetic as indicated by aCurie temperature not higher than zero degrees F. The coinage materialis characterized by high resistance to corrosion and high resistance totarnishing when handled in service. Further, the coins produced arehighly resistant to the kinds of wear which are encountered in coinageservice and thus have the potential for long service life. It is foundthat the coins and coinage strip contemplated in accordance with theinvention have a hardness in the annealed condition of about 60 RockwellB. The material hardens under cold working such that the hardness after10% cold work is about Rockwell B, after 25% cold work is about 102Rockwell B, and after 50% cold work is about 107 Rockwell B. The coldworked material can be annealed at temperatures of about 1300 F. toabout 2000 F. for about 10 to about 40 minutes, eg., about 1750 F. forabout 20 minutes. In producing Coins from the material, it is desirableto cold work annealed strip about 20% to provide a hardness of aboutRockwell B for the blanking operation. The blanks are then formed andare annealed in a nonoxidizing atmosphere to a hardness of about 60Rockwell B after which the blanks are embossed. In the embossingoperation, the hardness is increased to about 100 Rockwell B. The coinstake a sharp impression from the embossing dies and it is found that diewear is not excessive but is about on the same order as is encounteredwith a 75% copper, 25% nickel alloy currently employed in the productionof the U.S. tive cent piece.

The special combinations of resistivity and Curie temperature obtainablein coinage materials produced in accordance with the invention areillustrated in the following Table I:

TABLE I Resistivity, ity,

Mierohmcentimeters C urie Temper- Percent Silicon P ereent Nickel Theimportance of controlling the silicon content of coinage materialscontemplated in accordance with the invention is illustrated by theproperties of an alloy strip outside the invention containing 95.2%nickel and 4.8% silicon. This alloy strip had a higher resistivity inthe same condition as given for the strips in Table I of 39.58microhm-centimeters and an unacceptably high Curie temperature of 25 F.

5 j The resistance of coinage materials produced in accordance with theinvention to the combined effects of wear and corrosion as compared to acupronickel alloy containing 75% copper, balance nickel, and to purenickel was demonstrated by an accelerated wear-corrosion test.

The accelerated wear-corrosion test consisted of continuously tumblingabout 25 test coins in a baffled ceramic drum having a capacity of abouttwo gallons containing about 15 pounds of a solid charge comprisingkeys, pennies, 2 inch squares of leather, corks, canvas, rough-edgedHastelloy C shot and a solution f artificial perspiration comprising 40grams NaCl, 5 grams Nazi-1F04, 4 milliliters lactic acid, and distilledwater to make 4 liters of solution (as reported by S. I. Eisler and H.L. Faigen, Investigation of Synthetic Fingerprint Solutions, Corrosion,Nace, August 1954). The coins were periodically cleaned and weighed. Theweight loss determined upon test coins in the accelerated wearcorrosiontest is depicted in the accompanying drawing. The results indicate that,after 190 hours in the accelerated test, test coins made of thenickel-silicon alloy of the present invention displayed a wearresistance nearly 21/2 times better than test coins made of a standard75% copper-25% nickel coinage alloy and displayed a resistance to thecombined effects of wear and corrosion about 11/2 times better than purenickel test coins. It further can be said that the test coins made ofthe special nickel-silicon alloy displayed a resistance to the effectsof combined wear and corrosion on the order of 41/2 times better thancurrent U.S. silver alloy coinage. The weight loss suffered by thenickel-silicon alloy test coins was at a projected rate of only about1.5 milligrams per year as indicated in the accelerated test.

In `manufacturing the coinage material contemplated in accordance withthe invention, conventional air melting practice may Vbe employed, forexample, the air induction furnace is quite satisfactory. The followingmelting practice employing an air induction furnace has been foundcompletely satisfactory:

(l) Charge high puritynickel material such as electrolytic nickel withabout 0.05% nickel oxide.

(2) Melt down and heat to about 2700o F.

(3) Hold at temperature for about three minutes to permit reactionbetween -the nickel oxide and reactive impurities present.

(4) Add a silicon deoxidizing addition amounting to 0.05 by weight ofthe charge.

(5) Permit the melt to cool until it starts to freeze and add siliconmetal slowly. The addition of silicon is exothermic and cooling of themelt is helpful to compensate for the temperature increase in the meltdue to silicon addition.

(6) Adjust the bath temperature t0 about 2575 F.

(7) Deoxidize the melt by plunging about 0.05% aluminum metal and thenadd Iabout 0.05 magnesium as a nickel alloy containing about magnesium.

(8) Adjust the melt temperature to about 2575 F. and cast into ingotmolds.

(9) Heat the ingots to about 2100 F. and forge.

(10) Reheat the forged ingots to about 2l00 F. and hot roll from about0.5 inch to about 0.15 inch.

(11) Cold work the hot rolled strip without annealing to about 0.07inch.

(12) Anneal at about 1750 F. for about 5 to 10 minutes in `a protectiveatmosphere.

(13) Cold roll to about 0.065 inch (about 10% cold Work) for blanking.

It is desirable to clean the surface of the ingot before hot working andof the hot rolled strip before cold rolling by conventional means ysuchas pickling, grinding, etc. In annealing the coinage material,protective atmospheres such `as dry hydrogen, cracked ammonia, driedpartially combusted natural gas, a dry gas mixture containing aboutnitrogen and 10% hydrogen, etc., may be employed.

Investigations of other nickel-base alloy systems have demonstrated thatthe coinage material contemplated in accordance with the presentinvention possesses a unique combination of properties to a remarkableextent. These investigations have included nickel-base alloy systemswherein vanadium, aluminum, titanium, chromium and copper have beenemployed in place of, or in combination with, silicon. It has been foundthat all of these alloy systems have possessed undesirable properties invarious respects as compared to the essentially binary nickelsiliconalloy coinage material contemplated in accordance with the presentinvention. Thus, titanium and aluminum form stable compounds, believedto be NigTi and NisAl, respectively, and the resulting alloys aremagnetic, age-hardenable and provide poor coinage die life. Accordingly,the resulting alloys are unsatisfactory as coinage materials.

It was also found that chromium additions to nickel quickly raiseelectrical resistivity to unacceptable high levels for coinage purposesand produce hard alloys which lower coinage die life. Certain alloycombinations in the nickel-silicon-vanadium alloy system containingabout 5% to less than 6.5% silicon plus vanadium can give certaindesirable properties for coinage purposes, but these combinations do notprovide a combination of a resistivity less than 40 microhal-centimeterswith a Curie point less than zero degrees F. Furthermore, these alloysare attended by serious practical drawbacks making them much lesssatisfactory than the special nickelsilicon coinage materials to whichthe present invention is directed. Thus, vanadium of acceptable purityto meet requirements is very expensive and vanadium-containingferroalloys cannot be used because the accompanying iron is ruinous tothe Curie temperature and resistivity properties required in nickelalloy coinage materials. In addition, vanadium provides practicaldiflculties in air melting since vanadium additions of the requisiteorder generate a sticky slag which is very di'licult to handle. Thisproblem can be overcome by vacuum melting and/ or vacuum treating, butthese expedients raise the cost of melting very considerably. Thisfactor, coupled with the high cost of vanadium metal, make coinagematerials produced from the alloys uneconomic. Alloys within thisgrouping together with the electrical resistivity and Curie temperaturesdeveloped in strip produced therefrom in the annealed condition aregiven in the following Table II:

TABLE II Percent Percent Percent Resistivity Curie Alloy No. NickelSilicon Vanadium Microhm- Temperacentimeters ture, F.

93. 1 1. 55 4. 40 48. 95 25C 93. 5 2. 12 3.80 43. 56 5A 93. 9 3.16 2. 039. 51 35B It will be seen from `the foregoing Table II that the givenproperties of these nickel-silicon-vanadium alloys are decidedlyinferior to the same properties of the binary nickel-silicon alloycoinage materials contemplated in accordance with the invention. Forexample, Alloy C, the only alloy having a resistivity below 40microhmcentimeters, had an impermissibly high Curie temperature of 35 F.Temperatures of this order and lower temperatures are encountered underordinary ambient conditions and would cause a coin made from the alloyto become magnetic whereupon it would be rejected by a vending machine.

Certain nickel-silicon-copper alloys can possess acceptable combinationsof resistivity and Curie temperature for use as coinage materials. Analloy strip containing 4.53% silicon, 4.9% copper, balance nickel, hadan undesirably high resistivity of 43.67 microhm-centimeters and a Curietemperature of minus 88 F. However, the compositional ranges in thissystem which will provide the requisite combinations of resistivity andCurie ternperature are so narrow that it is not practical to employ themcommercially for the production of coinage materials. Thus, even veryminor variations in composition can cause unacceptably wide increases inboth Curie temperature and resistivity with the result that a largeproportion of scrap heats would be encountered in commercial operation,with concomitant increases in cost.

Coins contemplated in accordance with the invention are accepted withoutadjustment by the coin-discriminating devices currently employed invending machines lto accept the U.S. live cent piece. It is found,however, that adjustment of the vending machine discriminating circuitsis required before coins made in accordance with the invention can beaccepted by the discriminating circuits employed in vending machines toaccept valid U.S. ten cent, twenty-five cent, fifty cent, and one dollarcoins. This latter factor reilects the substantially high resistivity ofthe coinage material contemplated in accordance with the invention ascompared to the low resistivity, e.g., about 2 microhm-centimeters, ofthe 90% silver-10% copper alloy currently employed for U.S. silvercoins.

Although the present invention has been described in conjunction withpreferred embodiments, it is to be understood that modifications andvariations may be resorted to without departing from the spirit andscope of the invention as those skilled in the art will readilyunderstand. Such modifications and variations are considered to bewithin the purview and scope of the invention and appended claims.

We claim:

1. As a new article of manufacture, coinage strip made of an alloyconsisting essentially of about 4.85% to about 5.15% silicon, with thebalance of the alloy being essentially nickel, said strip beingcharacterized by a Curie temperature not higher than about zero degreesF., a hardness in the annealed condition of about 60 Rockwell B and inthe embossed condition of about 10() Rockwell 13, good hot workabilityand cold workability, high resistance to corrosion, tarnishing and wear,good embossability, a resistivity not exceeding about 40microhm-centimeters, a density of about 8.6 grams per cubic centimeter,and by a bright silvery color.

2. As a new article of manufacture, a coin made of an alloy consistingessentially of about 4.85% to about 5.15% silicon, with the balance -ofthe alloy being essentially nickel, said coin 4being characterized by aCurie temperature not higher than about zero degrees F., a hardness invthe embossed condition of about Rock- Well B, good hot workability andcold workability, high resistance to corrosion, tarnishing and wear,good embossability, a resistivity not exceeding about 40microhm-centimeters, a density of about 8.6 grams per cubic centimeter,and by a bright silvery color.

3. As a new article of manufacture, coinage material made of an alloyconsisting essentially of about 4.85% to about 5.6% silicon, with thebalance essentially nickel, said coinage material being characterized bya Curie temperature not higher than about zero degrees F., good hotworkability and cold workability, high resistance to corrosion,tarnishing and wear, and by a bright silvery color.

4. As a new article of manufacture, coinage material made of an alloyconsisting essentially of about 4.85% to about 5.15% silicon, with thebalance essentially nickel, said coinage material being characterized bya Curie temperature not higher than about zero degrees F., good hotworkability and cold workability, high resistance to corrosion,tarnishing and wear, and by a bright silvery color.

References Cited UNITED STATES PATENTS 1,057,755 4/1913 Marsh 75-1701,695,845 12/1928 Hallock 75-170 1,769,229 7/1930 Mandell 75-1702,510,801 6/1950 Chilowsky 75-170 DAVID L. RECK, Primary Examiner.

RICHARD O. DEAN, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,367,773 February 6, 1968 Pierre P. Turillon et al.

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column l, line 4l, "allows" should read alloys line 55, "acuate" shouldread acute A. Column 4, line 19, "slvery" should read silvery TABLE I,fourth column heading, cancel "ityf', second occurrence. Column 6, TABLEII,

first column, lines l, 2 and 3 thereof, insert A B Signed and sealedthis 23rd day of September 1969.

(SEAL) Attest:

EDWARD M.PLETCHER,JR. WILLIAM E. SCHUYLER, JR. Attesting OfficerCommissioner of Patents

